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Practical synchronous digital systems radiate electromagnetic energy on a number of narrow bands spread on the clock frequency and its harmonics, resulting in a frequency spectrum that, at certain frequencies, can exceed the regulatory limits for electromagnetic interference (e.g. those of the FCC in the United States, JEITA in Japan and the ...
In the US, FCC part 15 on unlicensed spread spectrum systems in the 902–928 MHz and 2.4 GHz bands permits more power than is allowed for non-spread-spectrum systems. Both FHSS and direct-sequence spread-spectrum (DSSS) systems can transmit at 1 watt, a thousandfold increase from the 1 milliwatt limit on non-spread-spectrum systems.
Mortimer Alan Rogoff (May 2, 1921 – August 1, 2008) was an American inventor, businessman, and author as well as an amateur photographer and radio operator. He is recognized for his work in spread spectrum technology which is the technology that modern cell phones and GPS systems are based on. He is also considered the grandfather of the ...
Hedy Lamarr (/ ˈ h ɛ d i /; born Hedwig Eva Maria Kiesler; November 9, 1914 [a] – January 19, 2000) was an Austrian-born American actress and inventor. After a brief early film career in Czechoslovakia, including the controversial erotic romantic drama Ecstasy (1933), she fled from her first husband, Friedrich Mandl, and secretly moved to Paris.
Although well publicized at the time, the system's enormous military potential was not developed until the late 1930s. Huff-duff allowed operators to determine the location of an enemy radio transmitter in seconds and it became a major part of the network of systems that helped defeat the threat of German U-boats during World War II. It is ...
Some of the problem came from amateurs using crude spark-transmitters that spread signals across a wide part of the radio spectrum. [1] In 1912 after the RMS Titanic sank, the United States Congress passed the Radio Act of 1912 [8] which restricted private stations to wavelengths of 200 meters or shorter (1500 kHz or higher). [9]
The invention of the cotton gin by American inventor Eli Whitney, combined with the widespread prevalence of slavery in the United States and U.S. settler expansion made cotton potentially a cheap and readily available resource for use in the new textile industry.
Direct-sequence spread-spectrum transmissions multiply the symbol sequence being transmitted with a spreading sequence that has a higher rate than the original message rate. Usually, sequences are chosen such that the resulting spectrum is spectrally white. Knowledge of the same sequence is used to reconstruct the original data at the receiving ...